The present invention relates to a method and an apparatus for the magnetic inspection of ferrous conduit for signs of wear.
Ferrous conduit, in the form of sections of pipe or continuous coil tubing, is used in numerous applications. For example, in an oil well, ferrous conduit extends from surface to the bottom of the well. Oil is lifted from the bottom of the well to surface by a screw pump, pump jack or other method. The screw pump is positioned at the bottom of the oil well and is turned by a drive unit positioned at the surface. The screw pump is connected to the drive unit by either sucker rods or co-rod that run the entire length of the conduit. The drivels unit rotates the sucker rods or co-rod to transfer torque to the screw pump.
When a screw pump has been operating for a period of time, wear patterns begin to develop on the conduit. The wear patterns experienced depend upon whether the rods connecting the screw pump and the drive unit are sucker rods or co-rods. Sucker rods come in finite lengths, usually 25 foot lengths. There are, therefore, joints every 25 feet where sucker rods are screwed together in end to end relation. As the sucker rod string rotates, the joints tend to wear a circumferential groove within the conduit. Co-rod continuous rod that runs the entire length of the conduit. As the co-rod rotates it tends to wear a longitudinal groove within the conduit.
If the conduit contains a flaw, such as a crack or a loss of metallic area, the conduit is susceptible to rupturing. As part of a program of preventative maintenance, the conduit is periodically inspected. Magnetic inspection apparatus have been developed for use in such preventative maintenance programs. An example of such a magnetic inspection apparatus is U.S. Pat. No. 5,671,155. This magnetic inspection apparatus induces magnetic fields in ferrous conduit. The changes in the induced magnetic field are then measured and signals are produced representative of those changes which are used to identify irregularities. The apparatus constructed in accordance with the teachings of the invention have, to date, only been suited for reliably detecting circumferential wear patterns. Such apparatus is not suited for reliably detecting longitudinal wear patterns.
What is required is a method and an apparatus for the magnetic inspection of ferrous conduit for signs of wear, that is capable of reliably detecting longitudinal wear patterns.
According to one aspect of the present invention there is provided an apparatus for the magnetic inspection of ferrous conduit for signs of wear which includes a housing having a first end, a second end and a conduit travel passage extending through the housing from the first end to the second end. At least one coil is positioned within the housing encircling the conduit travel passage. The coil is disposed at an angle to the conduit travel passage so as to create a transverse flux component. Sensor supports are positioned along the conduit travel passage encircled by the coil. At least one sensor array is mounted on the sensor supports. The sensor array is oriented to detect flux patterns which extend transversely relative to the conduit travel passage. A computer is in communication with the sensor array to receive and interpret signals from the sensor array.
The apparatus, as described above, is capable of detecting longitudinal wear patterns. It accomplishes such detection by using an angular oriented coil to create a transverse flux component and an array of sensors oriented to detect the transverse flux component. In order to avoid the necessity of multiple passes of conduit through the apparatus, it is preferred that the sensor supports and the sensor array be positioned to provide flux pattern detection over 360 degrees of the circumference.
Although beneficial results may be obtained through the use of the apparatus, as described above, it is preferred that two or more coils be used. Each of the two or more coils are disposed at a different angle in relation to the conduit travel passage. Sensor supports are positioned within each of the two or more coils. A sensor array is mounted on each of the sensor supports. With multiple coils, the coverage of the conduit is improved. One preferred configuration includes a first coil positioned within the housing encircling the conduit travel passage at a first angle and a second coil positioned within the housing encircling the conduit travel passage at a second angle. A first pair of sensor supports is positioned in parallel spaced relation on opposed sides of the conduit travel passage within the first coil. A second pair of sensor supports is positioned in parallel spaced relation on opposed sides of the conduit travel passage within the second coil. The second pair of sensor supports is offset by 90 degrees from the first pair of sensor supports.
Although beneficial results may be obtained through the use of the apparatus, as described above, in most applications it is desirable to inspect the conduit for both longitudinal wear patterns and circumferential wear patterns. Even more beneficial results may, therefore, be obtained when each sensor support includes a first sensor array and a second sensor array. The first sensor array is oriented to detect flux patterns which extend transversely relative to the conduit travel passage. The second sensor array is oriented to detect flux patterns which extend longitudinally relative to the conduit travel passage.
Although beneficial results may be obtained through the use of the apparatus, as described above, it is desirable to get the sensors as close as possible to the conduit in order to improve the sensitivity to a level where small defects or degree of wear can be detected. Even more beneficial results may, therefore, be obtained when the sensor supports are concave and are oriented to conform to the contour of conduit passing through the conduit travel passage.
Although beneficial results may be obtained through the i use of the apparatus, as described above, with a string of joined conduits joints are encountered at periodic intervals. Even more beneficial results may, therefore, be obtained when the sensor supports are mounted on springs. The springs enable the spacing between the sensor supports to adjust when passing over joints in conduit. This movement over joints can be enhanced by the addition of some further features. Even more beneficial results may be obtained when the sensor supports are mounted for limited pivotal movement about a centrally positioned transverse axis. Even more beneficial results may be obtained when the sensor supports have a wedge shaped inclined interior contact surface on at least one end.
Although beneficial results may be obtained through the use of the apparatus, as described above, it is important for sensor accuracy that the conduit always is properly aligned within the conduit travel passage. Even more beneficial results may be obtained when guide rollers are mounted to the housing surrounding the conduit travel passage to center housing around conduit passing through the conduit travel passage.
Although beneficial results may be obtained through the use of the apparatus, as described above, when conduit is pulled from an oil well during a field inspection, it is covered in oil. Even more beneficial results may, therefore, be obtained when a resilient annular wiper encircles the conduit travel passage and engages conduit prior to passing through the conduit travel passage to remove excess oil.
According to another aspect of the present invention there is provided a method for the magnetic inspection of ferrous conduit for signs of wear. A first step involves positioning a coil encircling a conduit travel path at an angle so as to create a transverse flux component. A second step involves positioning a sensor array along the conduit travel path encircled by the at least one coil, with the sensor array oriented to detect flux patterns which extend transversely relative to the conduit travel passage. A third step involves using a computer in communication with the sensor array to receive and interpret signals from the sensor array.
Although beneficial results may be obtained through the use of the method, as described above, it has been determined that the sensitivity of the apparatus to small imperfections can be enhanced when the amperage in the coil is kept constant.
Although beneficial results may be obtained through the use of the method, as described above, it has been determined that the large volume of data generated can best be handled when analog signals from the sensor are immediately converted to digital signals at their source prior to communication to the computer.